glutinous variety of millet
秫 refers specifically to a glutinous, sticky variety of millet. The meaning is narrow and concrete, centered on this particular grain.
秫 combines the grain radical 禾 with 术, which likely contributes a phonetic element. The character is used for a specific type of sticky millet.
The grain radical 禾 on the left tells you it's a plant, and the right side 术 looks a bit like a sticky, tangled mass. Picture a stalk of millet with extra-glutinous grains clinging together.
For ジョツ, imagine a sticky millet cake so dense it makes a heavy 'jots' sound when dropped: jots -> ジョツ, and the cake is made from glutinous millet.